1. Field of the Invention:
This invention relates to improved photographic silver halide emulsions. More particularly, it relates to photographic silver halide emulsions having increased speed and improved stability over emulsions made heretofore. Still more particularly, the invention relates to photographic silver halide emulsions chemically sensitized with organophosphine sulfides.
2. Prior Art:
It is known to chemically sensitize silver halide emulsions with a variety of chemical compounds, e.g., noble metal compounds, compounds providing labile sulfur or selenium, ethylene oxide polymers, etc. Chemical sensitization is considered to result from the formation of silver sulfide specks on the silver halide crystals resulting from the presense of labile sulfur or from the formation of silver specks on the silver halide crystals resulting from the presence of a reduction sensitizer, and is thereby differentiated from spectral sensitization, in which dyes are used to extend sensitivity into further regions of the spectrum, as is well known in the art.
The sensitizing activity of sulfur on silver halide emulsions has been well documented and those compounds which have been disclosed and which contribute labile sulfur in the system include thiosulfates, polythionates (S.sub.x O.sub.6 .dbd. where x = a whole number from 2 to 5 inclusive), e.g. tetrathionate, thioureas, e.g. allyl thiourea, mercapto compounds, etc. Reference may be had to: Mees and James, The Theory of the Photographic Process, Third Edition, The Macmillian Company, New York (1966). Sulfur sensitization occurs during digestion if labile sulfur compounds are present which decompose during the digestion stage to form the minute specks of silver sulfide on the silver halide crystals as described above. Heretofore, the labile sulfur compounds were initially present in the gelatin as naturally occurring substances or they were added in the form of the above ions to so-called inert gelatin used as the colloid carrier for the silver halide crystals to form the emulsion.
It is known to use organic phosphites in conjunction with labile sulfur to sensitize photographic silver halide emulsions and this is taught by Thurston, U.S. Pat. No. 3,338,712 patented Aug. 29, 1967.
Dunn, U.S. Pat. No. 3,297,446 patented Jan. 10, 1967 shows the use of organic tertiary phosphine compounds as antifoggants in silver halide emulsion systems using a synergistic sensitization combination of labile selenium and a noble metal.
Dunn, U.S. Pat. No. 3,442,653 patented May 6, 1960 teaches the use of triphenyl phosphine as an activating agent for non-labile selenium compounds in silver halide emulsions.
French Patent Pub. No. 2,201,484 describes trisubstituted organophosphine sulfides as supersensitizers for merocyanine dyes in the spectral sensitization of silver halide emulsions.